Absorbent articles, such as baby diapers, training pants, adult incontinence products and other such absorbent products include a topsheet that is closest to the wearer, an outer, moisture-impermeable backsheet, and an absorbent core. Disposable absorbent products have met with widespread acceptance in the marketplace for a variety of applications, including infant and adult incontinence care, in view of the manner in which such products can provide effective and convenient liquid absorption and retention while maintaining the comfort of the wearer. However, experience has shown that a need exists for more skin-friendly topsheet nonwovens. Examples of absorbent article constructions with which the present sheets can be used are disclosed in United States Patent Application Publications No. US 2006/0178650 and No. US 2010/0280479.
The nondurable, or fugitive, nature of synthetic surfactants used on all polyolefin topsheets and acquisition/distribution layers in use today play a role in absorbent product acquisition and rewet performance, but have a potential to compromise skin health. Synthetic surfactants are used as penetration aids in transdermal drug delivery. Synthetic surfactants washed from the nonwoven fibers during product use can increase the permeability of stratum corneum to all potential irritants, including the synthetic surfactant itself. Various emollient materials have be used in an attempt to restore barrier function to damaged skin, but a straightforward solution to the problem is to eliminate all synthetic surfactant from the nonwoven. In this invention we have identified potential chemistries for imparting wettability to polyolefin nonwovens and films, and teach how they can be applied effectively—without the use of any conventional synthetic surfactants and with the goal of promoting skin health.
Nonwovens made from polypropylene are hydrophobic. By application of suitable finishing treatments, it is possible to impart semi-durable hydrophilic properties to the nonwoven to achieve performance in liquid strike-through and liquid runoff that is required for their use in absorbent products. Suitable finishing treatments are typically proprietary blends of synthetic surfactant solutions which are commercially available, for example, from Schill & Seilacher AG (e.g. Silastol PHP 26, Silastol PHP 90, & Silastol 163), and Pulcra Chemicals (e.g. Stantex S 6327, Stantex S 6087-4, & Stantex PP 602). They are typically applied to spunbond nonwovens in the range of 0.004-0.006 gm solids/gm nonwoven (i.e. 0.4-0.6% wt/wt). An example of a synthetic surfactant that has been used widely used in commercially-available topsheet finishes would be Triton GR-5M, an anionic sulfosuccinate surfactant manufactured by Dow Chemical Company. Other types of surfactants used are based on fatty acid polyethylene glycol esters.
U.S. Pat. Nos. 5,938,649 and 5,944,705, Ducker, et al., disclosed an absorbent article containing aloe vera on the surface of the article contacting the wearer's skin to reduce rash. A preferred embodiment of this invention was an essentially water-free aloe vera in a waterless lubricant that was applied to an absorbent product independently of any surfactant finish on the topsheet nonwoven. Procter & Gamble commercialized a baby diaper in the late 1990's/early 2000's that contained an emollient lotion, applied in stripes, on a conventional topsheet nonwoven. U.S. Pat. No. 6,459,014 B1, Chmielewski and Erdman, mentions pH control agents such as citric acid and sodium citrate that can be added to a nonwoven topsheet in conjunction with an optional surfactant. However, all examples in this patent included synthetic surfactant and there was no discussion of how a nonwoven could be successfully treated with a surfactant-free solution of citric acid, or whether it could impart useful hydrophilic properties to the nonwoven. Furthermore, citric acid and sodium citrate are freely soluble in saline solution and would not provide a sufficiently durable finish to a topsheet nonwoven. More recently, in U.S. Pat. No. 6,936,345 B2, Wild et. al. describe a process for finishing nonwovens in such a way to meet requirements in regard to the permanence of the hydrophilic finish and be capable of providing an additional benefit, in this case suppression of the growth of bacteria. They described an aqueous antimicrobial finish containing a monoester of glycerol, a fatty acid and chitosan. The monoester of glycerol and the fatty acid are surface active ingredients that facilitate spreading of the antimicrobial finish on the nonwoven in the finishing process.
Salas, et al. in “Water-Wettable Polypropylene Fibers by Facile Surface Treatment Based on Soy Proteins”, ACS Appl. Mater. Interfaces 2013, 5, 6541-6548, reported on the modification of the wetting behavior of polypropylene nonwovens after adsorption of soybean proteins. Using Quartz Crystal Microgravimetry with thin, flat films of polypropylene, they confirmed a high affinity of adsorption for soy protein on polypropylene. A fast initial adsorption occurred in the order of seconds. This showed that adsorption of soy protein will indeed occur on polypropylene if the protein solution is forced to be in contact with the polymer surface. When extending their work to a polypropylene nonwoven, they noted that the hydrophobic nonwoven floated on the surface of the protein solution and prevented effective adsorption of the protein. To overcome this issue, they first immersed the polypropylene nonwovens in 2-propanol to clean the nonwoven, followed by an immersion into 1 mg/mL 2-propanol solution of cationic dioctadecyldimethylammonium bromide surfactant.